Fiber optic communications networks may increase the amount of information carried on an optical fiber by multiplexing different optical signals on different wavelengths using wavelength division multiplexing (WDM). In a WDM passive optical network (PON), for example, a trunk fiber carries optical signals at multiple channel wavelengths to and from an optical branching point and the branching point provides a simple routing function by directing signals of different wavelengths to and from individual subscribers. In this case, each subscriber may be assigned one or more of the channel wavelengths on which to send and/or receive data.
To transmit and receive optical signals over multiple channel wavelengths, an optical line terminal (OLT) in a WDM-PON may include a multi-channel transmitter optical subassembly (TOSA) and a multi-channel receiver optical subassembly (ROSA). One example of a TOSA includes a multiplexed laser array that combines multiple optical signals at multiple channel wavelengths. To provide the different channel wavelengths, tunable lasers may be used in the multi-channel TOSA and the wavelengths emitted by the tunable lasers change with changes in temperature. The desired accuracy or precision of the wavelengths in a WDM-PON often depends on the number and spacing of the channel wavelengths and may be controlled in the TOSA by controlling temperature. In a 100 G dense WDM (DWDM) system, for example, the temperature may need to be controlled within ±0.5° C. to maintain a wavelength precision of ±0.05 nm and the temperature range may need to be greater than 4° C. to provide the desired wavelength yield of the laser diodes.
To control the temperature of a tunable laser, one or more resistive heaters may be located proximate the laser, for example, on the same sub-mount as the laser. Such resistive heaters, however, are additional electronic components that take up additional space, increase cost, and may be inefficient in transferring heat to the laser. One challenge with such OLT transceiver modules is providing adequate temperature control of the laser array in a relatively small space and with a relatively low power budget.